Hi Curious, yeah filleting really doesn't seem to like the shapes you happen to be making here. I think it's a combination of bending plus that twisting effect I was talking about earlier.

The way to impose very regular surfaces on this would be to build it in some sections like this that are all of the same size:





So each of these surfaces are very simply structured, there isn't any sort of warping or twisting type effect on them.

They're squared up and they stick out past each other like this:



Then using Edit > Trim they can be cut against each other:



This type of structure should be vastly more reliable for filleting:



The thing you give up is direct control over the bending shape, since it's built for you by filleting. I'll see if I can give some tips on how that might be tweaked.

- Michael